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Met 10 Weather ProcessesJeff Gawrych

Temperature, Heat Transfer and Earth’s

Energy Balance

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Lecture OutlineLecture Outline

• Energy in the atmosphere

• Shortwave and longwave radiation

• Greenhouse effect

• Earth/atmosphere energy balance

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Why does the earth heat up?

• Incoming solar radiation is absorbed by the surface of the planet.

• The amount and intensity of the solar energy received is called insolation.

• Some areas get more insolation than others. E.g. The tropics are generally warmer than the polar regions.

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Heat

• Sensible Heat: he we feel• Latent Heat: The heat energy required to

change water from one state to another (e.g. water from vapor to a solid).

• “hidden” heat due to phase changes– E.g. Water has 3 phases– 1) Ice 2) Liquid 3) Vapor (gas)

• Latent heat of evaporationevaporation: – Heat lost to environment

• Latent heat of condensation: condensation: – Heat released to environment

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Earth’s Energy BalanceEarth’s Energy Balance

• A balance exists that keeps the planet from getting too hot or cold

– Energy entering top of atmosphere must equal Energy leaving top of atmosphereEnergy leaving top of atmosphere

– Energy entering the Earth’s surface must equal Energy leaving Earth’s surfaceEnergy leaving Earth’s surface

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There are three modes of energy transmission in the There are three modes of energy transmission in the atmosphere.atmosphere.

• Conduction: the transfer of energy in a substance by means of molecular excitation without any net external motion.

• Convection: the transfer of energy by mass motions within a fluid or gas, resulting in actual transport of energy.

• Radiation: the propagation of electromagnetic waves through space.

Energy transmissionEnergy transmission

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Electromagnetic radiation

• Radiation is the transfer of energy by rapid oscillations of electromagnetic fields.

• The most important general characteristic is its wavelength (), defined as the

crest-to-crest distance.• Radiation travels through space at the speed of light (3 x

108 m s-1).• All objects emit radiation!!!!• Amount of radiation absorbed/emitted depends on Temp.

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Short and longwave radiation• All objects emit radiation:

– Sun emits radiation mostly at shorter wavelengths; ultraviolet (UV) and visible:

– Earth emits radiation mostly at longer wavelengths; infrared (IR)

• Difference based on temperature of emitting body.

–(shortwave or solar radiation)

–(Longwave or terrestrial radiation)

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Atmospheric Greenhouse Atmospheric Greenhouse EffectEffect

• Essential for life as we know it!!!• The atmosphere absorbs some of the Earth’s outgoing

longwave radiation.– Atmosphere acts like a blanket

• Which atmospheric gases are most responsible for the Greenhouse Effect?

Water, Carbon Dioxide (COWater, Carbon Dioxide (CO22))

• Runaway greenhouse effect– The addition of too many greenhouse gases that could possibly

lead to large-scale climate change (global warming)– It is analogous to closing a window, in that outgoing radiation

cannot escape.

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Incoming solar radiationIncoming solar radiation

• Each ‘beam’ of incoming sunlight can be either:– Reflected back to space: albedo=reflectivity

• Clouds• Atmosphere• Surface

– Earth’s Albedo is 30 %

– Or absorbed; either by atmosphere (e.g. clouds or ozone) or Earth’s surface.

– Or Scattered; This is why the sky is blue, or red, or whatever color. Whichever color you see if the most scattered wavelength (color) of visible light

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Earth’s Energy BalanceEarth’s Energy Balance

• The earth must stay in balance or else it would forever get hotter or colder.

Energy into the Earth/Atmosphere system

= Energy out of the Earth/Atmosphere

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